TECHNICAL FIELD
[0001] The invention relates to high intensity focused ultrasound, in particular to the
sonication of a moving target.
BACKGROUND OF THE INVENTION
[0002] Ultrasound is quickly becoming a desired approach for specific therapeutic interventions.
In particular, the use of high intensity focused ultrasound is currently being used
as an approach for thermal therapeutic intervention for uterine fibroids and has been
examined for possible uses in the treatment of liver, brain, prostate, and other cancerous
lesions. Ultrasound therapy for tissue ablation works by sonicating a tissue of interest
with high intensity ultrasound that is absorbed and converted into heat, raising the
temperature of the tissues. As the temperature rises coagulative necrosis of the tissues
may occurs resulting in immediate cell death. The transducers used in therapy can
be outside the body or be inserted into the body e.g. through blood vessels, urethra,
rectum etc.
[0003] In high intensity focused ultrasound an array of transducer elements are used to
form an ultrasonic transducer. Supplying alternating current electrical power to the
transducer elements causes them to generate ultrasonic waves. The ultrasonic waves
from each of the transducer elements either adds constructively or destructively.
By controlling the phase of alternating current electrical power supplied to each
of the transducer elements the focal point or volume into which the ultrasound power
is focused may be controlled.
[0004] Mechanical displacement of the HIFU transducer allows large displacements of around
10cm which is very convenient to center the focal point on the volume to treat. But
mechanical displacement is rather slow compared to the heating duration and the motion
speed of the target.
SUMMARY OF THE INVENTION
[0005] The invention provides for a therapeutic apparatus, a method of operating a therapeutic
apparatus and a computer program product in the independent claims. Embodiments are
given in the dependent claims.
[0006] In many clinical situations there may be external and/or internal motion of the subject
which is being sonicated. It is therefore beneficial to track the motion of a moving
target when sonicating. Present solutions include gating the ultrasound and sonicating
only when the target is in a particular location. It would be beneficial to be able
to track the position of a target and adjust the focus of the ultrasound to decrease
the time required to perform a sonication.
[0007] Mechanical steering of the focus may be too slow. Embodiments of the invention may
provide a means of electronically steering the focus during sonication to reduce the
total sonication time required for a moving target. Embodiments may enlarge the ablation
and track the target tissue during the High Intensity Focused Ultrasound (HIFU) heating
by using of electronic steering of the focal point. A deflection of the focal point
can be performed by changing the phase on each individual channel of the phased array
transducer to form a constructive interference at the wanted location. Electronic
steering is very fast since there is no speed limitation except the minimal time to
update electrical signal. Thus electronic steering allows changing the location of
the focal point in typically less than a few milliseconds and it induces no perturbation
on thermal maps. But electronic steering of the focal point induces intensity decrease
as function of the amplitude of the deflection. As a consequence the electronic steering
is limited to a small displacement within a beam deflection zone to avoid excessive
intensity decreases especially since the remaining energy not deposited in the focus
is absorbed in some uncontrolled location in the patient.
[0008] A 'computer-readable storage medium' as used herein encompasses any tangible storage
medium which may store instructions which are executable by a processor of a computing
device. The computer-readable storage medium may be referred to as a computer-readable
non-transitory storage medium. The computer-readable storage medium may also be referred
to as a tangible computer readable medium. In some embodiments, a computer-readable
storage medium may also be able to store data which is able to be accessed by the
processor of the computing device. Examples of computer-readable storage media include,
but are not limited to: a floppy disk, punched tape, punch cards, a magnetic hard
disk drive, a solid state hard disk, flash memory, a USB thumb drive, Random Access
Memory (RAM), Read Only Memory (ROM), an optical disk, a magneto-optical disk, and
the register file of the processor. Examples of optical disks include Compact Disks
(CD) and Digital Versatile Disks (DVD), for example CD-ROM, CD-RW, CD-R, DVD-ROM,
DVD-RW, or DVD-R disks. The term computer readable-storage medium also refers to various
types of recording media capable of being accessed by the computer device via a network
or communication link. For example a data may be retrieved over a modem, over the
internet, or over a local area network. References to a computer-readable storage
medium should be interpreted as possibly being multiple computer-readable storage
mediums. Various executable components of a program or programs may be stored in different
locations. The computer-readable storage medium may for instance be multiple computer-readable
storage medium within the same computer system. The computer-readable storage medium
may also be computer-readable storage medium distributed amongst multiple computer
systems or computing devices.
[0009] `Computer memory' or 'memory' is an example of a computer-readable storage medium.
Computer memory is any memory which is directly accessible to a processor. Examples
of computer memory include, but are not limited to: RAM memory, registers, and register
files. References to 'computer memory' or 'memory' should be interpreted as possibly
being multiple memories. The memory may for instance be multiple memories within the
same computer system the memory may also be multiple memories distributed amongst
multiple computer systems or computing devices.
[0010] 'Computer storage' or 'storage' is an example of a computer-readable storage medium.
Computer storage is any non-volatile computer-readable storage medium. Examples of
computer storage include, but are not limited to: a hard disk drive, a USB thumb drive,
a floppy drive, a smart card, a DVD, a CD-ROM, and a solid state hard drive. In some
embodiments computer storage may also be computer memory or vice versa. References
to 'computer storage' or 'storage' should be interpreted as possibly being multiple
storage devices. The storage may for instance be multiple storage devices within the
same computer system or computing device. The storage may also be multiple storages
distributed amongst multiple computer systems or computing devices.
[0011] A 'processor' as used herein encompasses an electronic component which is able to
execute a program or machine executable instruction. References to the computing device
comprising "a processor" should be interpreted as possibly containing more than one
processor or processing core. The processor may for instance be a multi-core processor.
A processor may also refer to a collection of processors within a single computer
system or distributed amongst multiple computer systems. The term computing device
should also be interpreted to possibly refer to a collection or network of computing
devices each comprising a processor or processors. Many programs have their instructions
performed by multiple processors that may be within the same computing device or which
may even be distributed across multiple computing devices.
[0012] A 'user interface' as used herein is an interface which allows a user or operator
to interact with a computer or computer system. A 'user interface' may also be referred
to as a 'human interface device.' A user interface may provide information or data
to the operator and/or receive information or data from the operator. A user interface
may enable input from an operator to be received by the computer and may provide output
to the user from the computer. In other words, the user interface may allow an operator
to control or manipulate a computer and the interface may allow the computer indicate
the effects of the operator's control or manipulation. The display of data or information
on a display or a graphical user interface is an example of providing information
to an operator. The receiving of data through a keyboard, mouse, trackball, touchpad,
tactile screen, pointing stick, graphics tablet, joystick, gamepad, webcam, headset,
gear sticks, steering wheel, pedals, wired glove, dance pad, remote control, one or
more buttons, one or more switches, and an accelerometer are all examples of user
interface components which enable the receiving of information or data from an operator.
[0013] A 'hardware interface' as used herein encompasses an interface, which enables the
processor of a computer system to interact with and/or control an external computing
device and/or apparatus. A hardware interface may allow a processor to send control
signals or instructions to an external computing device and/or apparatus. A hardware
interface may also enable a processor to exchange data with an external computing
device and/or apparatus. Examples of a hardware interface include, but are not limited
to: a universal serial bus, IEEE 1394 port, parallel port, IEEE 1284 port, serial
port, RS-232 port, IEEE-488 port, Bluetooth connection, Wireless local area network
connection, TCP/IP connection, Ethernet connection, control voltage interface, MIDI
interface, analog input interface, and digital input interface.
[0014] Magnetic Resonance (MR) data is defined herein as being the recorded measurements
of radio frequency signals emitted by atomic spins by the antenna of a Magnetic resonance
apparatus during a magnetic resonance imaging scan. A Magnetic Resonance Imaging (MRI)
image is defined herein as being the reconstructed two or three dimensional visualization
of anatomic data contained within the magnetic resonance imaging data. This visualization
can be performed using a computer.
[0015] Thermographic data is data which is descriptive of the spatially dependent temperature
within at least a portion of a subject. For example ultrasound data acquired by a
diagnostic ultrasound system or magnetic resonance data may be or comprise thermographic
data.
[0016] Magnetic Resonance thermometry data is defined herein as being the recorded measurements
of radio frequency signals emitted by atomic spins by the antenna of a Magnetic resonance
apparatus during a magnetic resonance imaging scan which contains information which
may be used for magnetic resonance thermometry. Magnetic resonance thermometry data
is an example of thermographic data. Magnetic resonance thermometry functions by measuring
changes in temperature sensitive parameters. Examples of parameters that may be measured
during magnetic resonance thermometry are: the proton resonance frequency shift, the
diffusion coefficient, or changes in the T1 and/or T2 relaxation time may be used
to measure the temperature using magnetic resonance. The proton resonance frequency
shift is temperature dependent, because the magnetic field that individual protons,
hydrogen atoms, experience depends upon the surrounding molecular structure. An increase
in temperature decreases molecular screening due to the temperature affecting the
hydrogen bonds. This leads to a temperature dependence of the proton resonant frequency.
[0017] The proton density depends linearly on the equilibrium magnetization. It is therefore
possible to determine temperature changes using proton density weighted images.
[0018] The relaxation times T1, T2, and T2-star (sometimes written as T2*) are also temperature
dependent. The reconstruction of T1, T2, and T2-star weighted images can therefore
be used to construct thermal or temperature maps.
[0019] The temperature also affects the Brownian motion of molecules in an aqueous solution.
Therefore pulse sequences which are able to measure diffusion coefficients such as
a pulsed diffusion gradient spin echo may be used to measure temperature.
[0020] One of the most useful methods of measuring temperature using magnetic resonance
is by measuring the proton resonance frequency (PRF) shift of water protons. The resonant
frequency of the protons is temperature dependent. As the temperature changes in a
voxel the frequency shift will cause the measured phase of the water protons to change.
The temperature change between two phase images can therefore be determined. This
method of determining temperature has the advantage that it is relatively fast in
comparison to the other methods. The PRF method is discussed in greater detail than
other methods herein. However, the methods and techniques discussed herein are also
applicable to the other methods of performing thermometry with magnetic resonance
imaging.
[0021] An 'ultrasound window' as used herein encompasses a window which is able to transmit
ultrasonic waves or energy. Typically a thin film or membrane is used as an ultrasound
window. The ultrasound window may for example be made of a thin membrane of BoPET
(Biaxially-oriented polyethylene terephthalate).
[0022] In one aspect the invention provides for a therapeutic apparatus comprising a high-intensity
focused ultrasound system comprising an ultrasound transducer. The ultrasound transducer
has an electronically adjustable focus. The ultrasound transducer may comprise multiple
transducer elements. The amplitude and in particular the phase of alternating current
electrical power provided to the individual elements making up the ultrasound transducer
enables the focus to be electronically adjusted. The ultrasound generated by each
element adds either constructively or destructively with the ultrasound from other
elements. By controlling the phase this may be used to deflect or adjust the location
of the focus. The high-intensity focused ultrasound system has a beam deflection zone.
The ultrasound transducer is configured for generating acoustic power when supplied
with alternating electrical current power. When the ultrasound transducer comprises
multiple transducer elements these elements may be configured for generating acoustic
power with a controllable phase. The intensity of the ultrasound at the electronically
adjustable focus divided by the acoustic power emitted is above a predetermined threshold
within the beam deflection zone. In other words the beam deflection zone is a zone
where the intensity at the focus divided by the acoustic power is above the predetermined
threshold. As the beam is deflected electronically the intensity at the focus divided
by the acoustic power may decrease. If the electronically adjustable focus is diverted
from the natural focus too far then the intensity at the focus divided by the acoustic
power will be greatly reduced.
[0023] A beam deflection zone essentially defines a region where the ultrasound at the location
of electronically adjustable focus is sufficiently powerful to be useful for sonicating
a target. The therapeutic apparatus further comprises a memory for storing machine
executable instructions. The therapeutic apparatus further comprises a processor configured
for controlling the therapeutic apparatus. Execution of the machine executable instructions
causes the processor to receive real time medical data. The real time medical data
is descriptive of the location of a moving target. By real time it is meant that the
location of the moving target is accurate within a predetermined time. That is to
say that the real time medical data is useful for identifying a current location of
the moving target. The real time medical data is used to target the moving target.
If the moving target is in a different location or in a location greater than a predetermined
distance then the real time medical data is not useful for identifying the location
of the moving target. Execution of the machine executable instructions further causes
the processor to adjust the electronically adjustable focus to target the moving target
using the real time medical data. Execution of the machine executable instructions
causes the processor to sonicate the moving target when the moving target is within
the beam deflection zone. In some embodiments the moving target is continually sonicated
when the moving target is within the beam deflection zone. This embodiment may be
beneficial because the moving target is sonicated for a longer duration than if the
sonication is only gated when the moving target is in a particular location. This
may have the advantage of being able to perform the sonication more rapidly.
[0024] In another embodiment the moving target is located at least partially using real
time tracking of the target within the real time medical data. The real time medical
data may describe the location of the target with a predetermined delay. The real
time tracking may use a model or predict the trajectory of the target based on previous
trajectory or behavior of the target. This embodiment may be beneficial because it
allows more accurate determination of the location of the moving target and therefore
more accurate targeting during sonication.
[0025] In another embodiment execution of the instructions causes the processor to receive
a motion tracking model. The motion tracking model is configured for predicting the
location of the moving target using the real time medical data. In some embodiments,
the motion tracking model is adapted or modified based on the motion of the target
zone. As the moving target is tracked the motion tracking model could be adapted or
modifed using the real time medical data.
[0026] The electronically adjustable focus is adjusted using the predicted location of the
moving target. Essentially the real time medical data is used as an input to the motion
tracking model which outputs a predicted location. The electronically adjustable focus
is then adjusted to the predicted location. Many types of motion within a subject
such as respiration are periodic or repeat over different timescales. The motion of
an internal anatomy can be therefore predicted by measuring various anatomical parameters.
For example the position of the diaphragm is useful in predicting the location of
various organs within the thoracic cavity. The beating of a subject's heart may also
cause the dislocation of certain anatomical features. Models for predicting the location
of internal anatomical features are known in the art. Such a known model could be
used and also adapted to the individual patient. The adaptation could be done using
measurements that capture the motion of the organs of interest before starting therapy.
[0027] In another embodiment the moving target comprises at least one localized volume.
A localized volume as used herein is a volume of a predetermined size. For instance
the high-intensity focused ultrasound system may be used to target a single point
within a subject. However, the high-intensity focused ultrasound system does produce
sonication within a finite difference. In some embodiments the localized volume is
the smallest volume that the high-intensity focused ultrasound system may sonicate.
[0028] In another embodiment the moving target comprises multiple localized volumes. The
electronically adjustable focus is targeted to the moving target by specifying a sequence
of localized volumes chosen from the multiple localized volumes. Execution of the
instructions further causes the processor to determine the sequence in accordance
with the real time medical data. In other words the moving target may comprise multiple
locations to be sonicated. Not all of these multiple localized volumes may be within
the beam deflection zone. Therefore the real time medical data may be used to determine
which of the multiple localized volumes should be sonicated. This embodiment may be
advantageous because it may allow the more rapid sonication of the moving target because
the localized volumes to be sonicated can be determined in real time.
[0029] In another embodiment Execution of the instructions further causes the processor
to receive an ultrasonic calibration. The ultrasonic calibration is descriptive of
the spatially dependent intensity of the ultrasound at the electronically adjustable
focus within the beam deflection zone. In other words the ultrasonic calibration contains
data which is descriptive of how strong or intense the focused ultrasound is within
different locations of the beam deflection zone. Execution of the instructions further
causes the processor to determine a sonication duration for each localized volume
in accordance with the ultrasonic calibration and the real time medical data. The
real time medical data and the ultrasonic calibration can be used to determine how
long a particular localized volume should be sonicated. This is important because
some sonication points may be within the deflection zone for a shorter period of time
and some points may receive more ultrasonic energy due to the location within the
beam deflection zone. Determining a sonication duration for each localized volume
is therefore beneficial to perform a better control of the temperature rise and/or
thermal dose delivery of the moving target. This control can be set to reach either
a temperature rise and/or thermal dose delivery uniform over the target or any predefine
delivery distribution over the target such as a distribution reducing the total energy
to emit. In another embodiment the moving target comprises at least one path. As used
herein a path is a continuous volume which may be sonicated by moving the electronically
adjustable focus in one or more directions.
[0030] In another embodiment the electronically adjustable focus follows a trajectory along
the at least one path. Execution of the instructions further causes the processor
to determine the trajectory in accordance with the real time medical data. In this
embodiment the electronically adjustable focus is adjusted to sonicate along a trajectory,
however the portion of the trajectory which is sonicated needs to be within the beam
deflection zone. This may be beneficial because the trajectory may be more rapidly
sonicated.
[0031] In another embodiment execution of the instructions further causes the processor
to receive an ultrasonic calibration. The ultrasonic calibration is descriptive of
the spatially dependent intensity of the ultrasound at the electronically adjustable
focus with the beam deflection zone. Each of the at least one path is divided into
portions. Execution of the instructions further causes the processor to determine
a sonication duration in accordance with the ultrasonic calibration and the real time
medical data for each of the portions. The therapeutic apparatus is configured to
sonicate each of the portions for the sonication duration. The benefits of this embodiment
are equivalent to many of the benefits for the embodiment where a sonication duration
is determined for one or more localized volumes.
[0032] In another embodiment the location of the moving target is predicted using dynamical
analysis of the real time medical imaging data. In dynamic analysis the motion may
be deduced from an optical flow method. Segmentation of the image may be performed
based on the detection of contours. Optical flow is based on cross-correlation between
two images from a dataset to identify matching locations of each voxel. This method
has the advantage that it is relatively fast and gives displacement of each voxel
rather than displacement of tissue contour.
[0033] In another embodiment the real time medical data is real time medical image data.
Execution of the instructions further causes the processor to acquire the real time
medical image data using the medical imaging system.
[0034] In another embodiment the medical imaging system is a magnetic resonance imaging
system.
[0035] In another embodiment the medical imaging system is a diagnostic ultrasound imaging
system. The diagnostic ultrasound imaging system may have an additional transducer
for making diagnostic ultrasound measurements. In yet other embodiments the transducer
for the diagnostic ultrasound system uses either a diagnostic ultrasound transducer
built into the ultrasound transducer of the high-intensity focused ultrasound system.
[0036] In another embodiment the medical image data comprises motion data and real time
thermographic data. The moving target is located using the motion data.
[0037] In another embodiment the sonication of the moving target is controlled in accordance
with the thermographic data. For instance the thermographic data may be magnetic resonance
thermometry data. Ultrasound imaging techniques may also be used to acquire temperature
data. The acquisition of real time thermographic data enables the calculation of a
thermal dose delivered to a region of the subject. Regions that have been under-sonicated
may be sonicated more or given preference for sonication and regions which have been
fully sonicated can be left out for further sonication. This has the advantage of
making the sonication more efficient.
[0038] In another aspect the invention provides for a method of operating a therapeutic
apparatus. The therapeutic apparatus comprises a high-intensity focused ultrasound
system comprising an ultrasound transducer. The ultrasound transducer has an electronically
adjustable focus. The high-intensity focused ultrasound system has a beam deflection
zone. The ultrasound transducer is configured for generating acoustic power when supplied
with alternating current electrical power. The intensity of ultrasound at the electronically
adjustable focus divided by the acoustic power emitted is above a predetermined threshold
within the beam deflection zone. The method comprises the step of receiving real time
medical data. The real time medical data is descriptive of the location of the moving
target. The method further comprises the step of adjusting the electronically adjustable
focus to target the moving target using the real time medical data. The method further
comprises the step of sonicating the moving target when the moving target is within
the beam deflection zone. The benefits of this method have been previously discussed.
[0039] In another aspect the invention provides for a computer program product comprising
machine executable instructions for operating a therapeutic apparatus. The therapeutic
apparatus comprises a high-intensity focused ultrasound system comprising an ultrasound
transducer. The ultrasound transducer has an electronically adjustable focus. The
high-intensity focused ultrasound system has a beam deflection zone. The ultrasound
transducer is configured for generating acoustic power when supplied with alternating
current electrical power. The intensity of ultrasound at the electronically adjustable
focus divided by the acoustic power emitted is above a predetermined threshold within
the beam deflection zone. The therapeutic apparatus further comprises a processor
configured for controlling the therapeutic apparatus. Execution of the machine executable
instructions causes the processor to receive real time medical data. Execution of
the machine executable instructions further causes the processor to adjust the electronically
adjustable focus to target the moving target using the real time medical data. Execution
of the machine executable instructions further causes the processor to sonicate the
moving target when the moving target is within the beam deflection zone. The benefits
of this computer program product have been previously discussed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0040] In the following preferred embodiments of the invention will be described, by way
of example only, and with reference to the drawings in which:
Fig. 1 shows a flow chart which illustrates a method according to an embodiment of
the invention;
Fig. 2 shows a flow chart which illustrates a method according to a further embodiment
of the invention;
Fig. 3 illustrates a therapeutic apparatus according to an embodiment of the invention;
Fig. 4 illustrates a therapeutic apparatus according to a further embodiment of the
invention;
Fig. 5 illustrates a therapeutic apparatus according to a further embodiment of the
invention;
Fig. 6 shows a plot of the normalized intensity of ultrasound generated by a high-intensity
focused ultrasound sensor as a function of deflection perpendicular to the beam axis;
Fig. 7 shows a plot of the normalized intensity of ultrasound generated by a high-intensity
focused ultrasound sensor as a function of deflection along the beam axis;
Figs. 8A, 8B, 8C, 8D, and 8E illustrate a subject with a moving target;
Figs. 9A, 9B, 9C, 9D, and 9E show a top view of the motion shown in Figs. A8 through
8E;
Fig. 10 illustrates a planar representation of linear periodic motion;
Fig. 11 illustrates the sonication time for the periodic motion shown in Fig. 10;
Fig. 12 illustrates a planar representation of a curved periodic motion trajectory;
Fig. 13 illustrates the sonication time for the periodic motion shown in Fig. 12;
Fig. 14 illustrates a planar representation of linear periodic motion with five sonication
points;
Fig. 15 illustrates the sonication time for the periodic motion shown in Fig. 14;
Fig. 16A, 16B, 16C, 16D, and 16E illustrate a subject with a moving target;
Fig. 17 is analogous to figure 14, except that there is higher energy deposition in
each point;
Fig. 18 illustrates the sonication time for the periodic motion shown in Fig. 17;
Fig. 19 shows the number of point to sonicated during each part time part of the cycle
for the example shown in Figs. 17 and 18;
Fig. 20 is analogous to figure 17, except that multiple points are sonicated simultaneously;
Fig. 21 illustrates the sonication time for the periodic motion shown in Fig. 20;
Fig. 22 is analogous to Fig. 20, except that the sonication paths are curved;
Fig. 23 illustrates the sonication time for the periodic motion shown in Fig. 23;
Fig. 24A, 24B, 24C, 24D, and 24E illustrate a subject with a moving target;
Fig. 25A, 25B, 25C, 25D, and 25E illustrate a subject with a moving target;
Fig. 26A, 26B, 26C, 26D, and 26E illustrate a subject with a moving target; and
Fig. 27 shows an example of sonications for continuous linear displacement;
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0041] Like numbered elements in these figures are either equivalent elements or perform
the same function. Elements which have been discussed previously will not necessarily
be discussed in later figures if the function is equivalent.
[0042] Fig. 1 shows a flow diagram which illustrates a method according to an embodiment
of the invention. In step 100 the method starts. Next in step 102 real medical data
is received. Next in step 104 the electronically adjustable focus is adjusted to target
the moving target using the real time medical data. Next in step 106 the target is
sonicated when the moving target is within the beam deflection zone. This may also
include sonicating a portion of the target which is within the beam deflection zone.
Box 108 is a decision box. If the sonication is not finished then the method returns
to step 102. Steps 102-106 are repeated in a continuous loop until the sonication
is finished. In this way real time medical data is received and used to continually
adjust the sonication. When the sonication is finished then the method ends in step
110.
[0043] Fig. 2 shows a flow diagram which illustrates a further method according to an embodiment
of the invention. The method shown in Fig. 2 starts at block 200. Next in step 202
real time medical image data is acquired using a medical imaging system. In this case
the acquisition of real time medical data by a medical imaging system is equivalent
to receiving the real time medical data. Next in step 204 the electronically adjustable
focus is adjusted to target the moving target using the real time medical data. In
step 206 the target is sonicated when the moving target is within the beam deflection
zone. Again portions of the target which are within the beam deflection zone may be
sonicated also. Block 208 is a decision block. If the sonication is not finished then
steps 202, 204, and 206 are repeated in a loop until the sonication is finished. Next
in step 210 the method ends when the sonication is finished.
[0044] Fig. 3 illustrates a therapeutic apparatus 300 according to an embodiment of the
invention. In addition to the components, the embodiment shown in Fig. 4 comprises
a temperature treatment system which is a high-intensity focused ultrasound system
302 for sonicating a subject 301. The high-intensity focused ultrasound system is
mounted below a subject support 303. The subject 301 is resting on the subject support
303. The high-intensity focused ultrasound system comprises a fluid-filled chamber
304. Within the fluid-filled chamber 304 is an ultrasound transducer 306. Although
it is not shown in this figure the ultrasound transducer 306 may comprise multiple
ultrasound transducer elements each capable of generating an individual beam of ultrasound.
This may be used to steer the location of a sonication point 318 electronically by
controlling the phase and/or amplitude of alternating electrical current supplied
to each of the ultrasound transducer elements.
[0045] The ultrasound transducer 306 is connected to a mechanism 308 which allows the ultrasound
transducer 306 to be repositioned mechanically. The mechanism 308 is connected to
a mechanical actuator 310 which is adapted for actuating the mechanism 308. The mechanical
actuator 310 also represents a power supply for supplying electrical power to the
ultrasound transducer 306. In some embodiments the power supply may control the phase
and/or amplitude of electrical power to individual ultrasound transducer elements.
The ultrasound transducer 306 generates ultrasound which is shown as following the
path 312. The ultrasound 312 goes through the fluid-filled chamber 308 and through
an ultrasound window 314. In this embodiment the ultrasound then passes through a
gel pad 316. The gel pad is not necessarily present in all embodiments but in this
embodiment there is a recess in the subject support 303 for receiving a gel pad 316.
The gel pad 316 helps couple ultrasonic power between the transducer 306 and the subject
301. After passing through the gel pad 316 the ultrasound 312 passes through the subject
301 and is focused to a sonication point 318. The sonication point is understood to
be a finite volume or localized volume to which the ultrasound is focused. The sonication
point 318 is being focused within a moving target 320. The sonication point 318 may
be moved through a combination of mechanically positioning the ultrasonic transducer
306 and electronically steering the position of the sonication point 318.
[0046] The region marked 322 is the beam deflection zone. The beam deflection zone is a
region where the electronically adjustable focus 318 can be adjusted such that the
intensity of ultrasound at the electronically adjustable focus 318 divided by the
acoustic power emitted by the transducer 306 is above a predetermined threshold. In
this example the entire moving target 320 is within the beam deflection zone 322.
However, in other embodiments or instances only a portion of the moving target 320
may be within the beam deflection zone 322. Also for some time periods the moving
target may be entirely or partially within the beam deflection zone 322 and other
time instances it may be partially or completely out of the beam deflection zone 322.
[0047] The high intensity focused ultrasound system 302 is shown as being connected to a
hardware interface 326 of the computer 324. The hardware interface 326 is connected
to a processor 328. The hardware interface 326 enables the processor 328 to send and
receive data and commands to control the operation and function of the therapeutic
apparatus 300. The processor 328 is further connected to a user interface 330, computer
storage 332 and computer memory 334.
[0048] The computer storage 332 is shown as containing a treatment plan 340. The treatment
plan 340 may contain detailed instructions or controls for sonicating or specifying
the sonication of the moving target 320. The computer storage 332 is further shown
as containing real time medical data 342. The real time medical data 342 may be received
from some other instrument or device which is capable of generating the real time
medical data. For instance the therapeutic apparatus 300 may be connected or networked
to a medical imaging system. The computer storage 332 is further shown as containing
sonication control commands 344 that were generated using the real time medical data
342. The computer storage 332 is further shown as containing an ultrasonic calibration
346. The ultrasonic calibration is descriptive of the spatially dependent intensity
of ultrasound divided by the acoustic power emitted. Further shown in the computer
storage 332 is a set of sonication durations 348. The sonication durations 348 are
for different portions or parts of the moving target 320. They may have been calculated
using the ultrasonic calibration 346.
[0049] The computer memory 334 is shown as containing a control module 350. The control
module 350 contains computer executable code which enables the processor 328 to control
the operation and function of the therapeutic apparatus 300. The computer memory 334
is further shown as containing a sonication control command generation module 352.
The sonication control command generation module 352 contains computer executable
code which enables the processor 328 to generate the sonication control commands 344
using the real time medical data 342. The computer memory 334 is further shown as
containing a motion tracking module 354. This is an optional module in some embodiments
where the sonication command generation module 352 uses the motion tracking module
354 and the real time medical data 342 to predict the current location of the moving
target 320. This enables more accurate sonication of the moving target 320.
[0050] Fig. 4 shows a therapeutic apparatus 400 according to a further embodiment of the
invention. The therapeutic apparatus 400 shown in figure 4 is similar to the therapeutic
apparatus 300 shown in Fig. 3. The therapeutic apparatus 400 comprises a magnetic
resonance imaging system 402. The magnetic resonance imaging system comprises a magnet
404. The magnet 404 is a cylindrical type superconducting magnet with a bore 406 through
the center of it. The magnet has a liquid helium cooled cryostat with superconducting
coils. It is also possible to use permanent or resistive magnets. The use of different
types of magnets is also possible for instance it is also possible to use both a split
cylindrical magnet and a so called open magnet. A split cylindrical magnet is similar
to a standard cylindrical magnet, except that the cryostat has been split into two
sections to allow access to the iso-plane of the magnet, such magnets may for instance
be used in conjunction with charged particle beam therapy. An open magnet has two
magnet sections, one above the other with a space in-between that is large enough
to receive a subject: the arrangement of the two sections area similar to that of
a Helmholtz coil. Open magnets are popular, because the subject is less confined.
Inside the cryostat of the cylindrical magnet there is a collection of superconducting
coils. Within the bore 406 of the cylindrical magnet there is an imaging zone 408
where the magnetic field is strong and uniform enough to perform magnetic resonance
imaging.
[0051] Within the bore 406 of the magnet there is also a set of magnetic field gradient
coils 410 which are used for acquisition of magnetic resonance data to spatially encode
magnetic spins within the imaging zone 408 of the magnet 404. The magnetic field gradient
coils are connected to a magnetic field gradient coil power supply 412. The magnetic
field gradient coils 410 are intended to be representative. Typically magnetic field
gradient coils contain three separate sets of coils for spatially encoding in three
orthogonal spatial directions. A magnetic field gradient power supply 412 supplies
current to the magnetic field gradient coils 410. The current supplied to the magnetic
field coils is controlled as a function of time and may be ramped or pulsed.
[0052] Adjacent to the imaging zone 408 is a radio-frequency coil 414 for manipulating the
orientations of magnetic spins within the imaging zone 408 and for receiving radio
transmissions from spins also within the imaging zone. The radio-frequency coil may
contain multiple coil elements. The radio-frequency coil may also be referred to as
a channel or an antenna. The radio-frequency coil 414 is connected to a radio frequency
transceiver 416. The radio-frequency coil 414 and radio frequency transceiver 416
may be replaced by separate transmit and receive coils and a separate transmitter
and receiver. It is understood that the radio-frequency coil 414 and the radio-frequency
transceiver 416 are representative. The radio-frequency coil 414 is intended to also
represent a dedicated transmit antenna and a dedicated receive antenna. Likewise the
transceiver 416 may also represent a separate transmitter and receivers.
[0053] The computer storage 332 is shown as additionally containing a pulse sequence 420.
A pulse sequence as used herein encompasses a set of instructions which enables the
processor 328 to control the magnetic resonance imaging system 402 to acquire the
magnetic resonance data 424. The computer storage 332 is further shown as containing
magnetic resonance data 424 that was acquired using the magnetic resonance imaging
system 402. The magnetic resonance data 424 is the real time medical data in this
embodiment. The computer storage 332 is further shown as containing a magnetic resonance
thermometry pulse sequence 422. The magnetic resonance thermometry pulse sequence
422 is a pulse sequence which enables the magnetic resonance imaging system 402 to
acquire magnetic resonance thermometry data which comprises magnetic resonance thermometry
data. The computer storage 332 is further shown as containing a magnetic resonance
image 426 that has been reconstructed from the magnetic resonance data 424. The computer
storage 332 is further shown as containing a temperature map 428 that has been reconstructed
from the magnetic resonance data 424. In this case the magnetic resonance data comprises
magnetic resonance thermometry data. The computer memory 334 is further shown as containing
an image reconstruction module 430 which was used for reconstructing the magnetic
resonance data 424 into the magnetic resonance image 426. The computer storage 334
is further shown as containing a temperature mapping module 432 which was used to
reconstruct the temperature map 428 from the magnetic resonance data 424. In some
embodiments the sonication control command generation module 352 uses the magnetic
resonance image 426 and/or the temperature map 428 in generating the sonication control
commands 344. For instance the magnetic resonance image may be the real time medical
data and may provide an identification of the location of the moving target 320 within
the subject. As another example the temperature map 428 may be used for identifying
how long a particular region of the moving target 320 has been sonicated. This could
be used for adjusting the sonication durations 348. In some embodiments the computer
memory 334 contains an image segmentation module 434. The sonication control command
generation module 352 may use the image segmentation module 434 with the magnetic
resonance image 426 to identify the location of the moving target 320.
[0054] Fig. 5 shows a therapeutic apparatus 500 according to a further embodiment of the
invention. The embodiment shown in Fig. 5 is similar to the embodiment shown in Fig.
3. In Fig. 5 a diagnostic ultrasound system 502 has been added to the therapeutic
apparatus 500. A diagnostic ultrasound transducer 504 is incorporated into the ultrasound
transducer 306. In some alternative embodiments the diagnostic ultrasound transmission
504 is separate from the ultrasound transducer 306. The diagnostic ultrasound transducer
504 is connected to the diagnostic ultrasound system 502. The diagnostic ultrasound
system 502 is also connected to the hardware interface 326. The control module 350
in this embodiment is also adapted for controlling the diagnostic ultrasound system
502.
[0055] The computer storage 332 is shown as containing diagnostic ultrasound data 506. The
diagnostic ultrasound data 506 in this embodiment is equivalent to real time medical
data. The computer storage 332 is further shown as containing a diagnostic ultrasound
image 508. The diagnostic ultrasound image 508 was reconstructed from the diagnostic
ultrasound data 506. The computer memory 334 is further shown as containing an image
reconstruction module 510. The image reconstruction module 510 contains computer executable
code for reconstructing the diagnostic ultrasound image 508 from the diagnostic ultrasound
data 506. The computer memory 334 is further shown as containing image segmentation
module 512. The image segmentation module 512 contains computer executable code for
identifying the location of the moving target 320 within the diagnostic ultrasound
image 508. The sonication control command generation module 352 may use the image
segmentation module 512 to identify the location of the moving target 320 when it
is generating the sonication control commands 344.
[0056] Fig. 6 shows a plot of the normalized intensity of ultrasound generated by a high-intensity
focused ultrasound transducer. The plot on the x-axis is the deflection perpendicular
to the beam, which corresponds to the y or z-axis of the transducer 602. The y-axis
is the normalized intensity 604. The normalized intensity is the intensity of ultrasound
at the electronically adjustable focus divided by the acoustic power emitted by the
ultrasound transducer normalized by the intensity divided by the acoustic power at
the geometrical focus of the typical concave HIFU transducer. For non concave HIFU
transducer any other reference point such as the one generating the maximal intensity
divided by acoustic power can be used. The dashed line 606 shows the normalized intensity
at 50%. This may be one example of a predetermined threshold for which the normalized
intensity is above. The region 608 may be an example of a beam deflection zone defined
by the threshold 606.
[0057] Fig. 7 shows the normalized intensity 700 for deflection along the beam axis or the
x-axis. The x-axis is the beam deflection along the transducer's x-axis. The y-axis
is again the normalized intensity 604. The dashed line 606 shows the 50% normalized
intensity. This is used to define the beam deflection zone 704 in Fig. 7.
[0058] Mainly three strategies exist for the treatment of mobile organs by MR-HIFU. The
simple one consists to sonicate continuously independently of the motion. In that
case, the heating spreads along the uncontrolled trajectory of motion of the target
tissue. Alternatively, the sonication can be gated with the respiratory or the cardiac
cycle to achieve heating only at the target location, but the heating duty cycle is
usually too low to treat perfused organs such as liver or kidney. Alternatively the
focal point can be moved electronically to compensate the target tissue displacement
but the large focal point deflection required reduces the heating efficiency and restricts
the use of simultaneous volumetric heating also based electronic steering.
[0059] Embodiments of the invention may use the tissue displacement to minimize the required
electronic steering to achieve a more efficient heating in combination with volumetric
heating. For example if heating of a volumetric circle is to be achieved on an organ
moving along one direction, only displacement perpendicular to the motion direction
may be necessary to sonicate this circle.
[0060] Figs. 6 and 7 illustrate the intensity drop while using deflection perpendicular
to the beam axis (usually Foot-Head (FH) and -Left-Right (LR) direction) and along
the beam axis (usually Anterior-Posterior (AP) direction). The reference to normalized
the intensity is the intensity while focal point is located at the natural focus location
defined by the geometric center of the typically concave transducer (all channels
of the transducer in phase). However we can notice in particular case that the steering
of the focal point along the beam axis toward the transducer can induce intensity
increase (sometime up to 20%) because there is more energy at the proximity of the
transducer.
[0061] Figs. 6 and 7 show the maximal deflection (Fig. 6) perpendicular to the beam axis
and (Fig. 7) along the beam axis is typically defined by the threshold 50% of the
intensity at the natural focus location. In this example, the threshold to define
the maximal acceptable steering is usually taken to be 50% of the normalized intensity.
[0062] This maximal steering range is typically twice longer along the beam axis compared
to steering range perpendicular to the beam axis. If a steering is used to move the
focal point along the beam axis, thus the maximum steering range perpendicular to
the beam axis would be smaller. The Fig. 6 and 7 display the intensity drop along
two axes, but in practice this intensity drop is evaluated in 3D to process intensity
compensation for all location by applying higher electrical power level on the transducer.
[0063] The treatment of mobile organ such as kidney or liver is problematic since the target
tissue moves relative to the transducer which is usually in a fixed position attached
to the therapeutic platform. If the motion is not taken into account, the heating
induced by the static focal point is spread along the motion trajectory of the tissue
which makes the heating less efficient and the healthy tissue may also be ablated.
The first strategy proposed to overcome this issue was the use of sonications gated
on the cardiac or respiratory periodic cycle. In that case the location of the heating
is well localized but the heating remains relatively inefficient because the tissue
is heated during only a small fraction of the motion cycle. To overcome this low duty
cycle, the alternative solution consists to perform electronic steering to heat continuously
the same part of the target tissue by applying deflection equal to the motion.
[0064] However the amplitude of the motion can be as large as or even larger than the maximal
electronic steering range. For example, the upper part of the liver may move with
an amplitude of 4 cm along Foot to Head (FH) direction which is larger than the typical
steering range of HIFU systems of approximately 2 cm along this direction. In addition
if the full steering range capability is used to perform compensation of tissue motion,
high intensity power compensation factor has to be used to achieve the target intensity,
which leaves it impossible to perform additional steering for enlarging the heated
volume via volumetric sonication.
[0065] Embodiments of the invention may use the tissue or target motion to enlarge the energy
delivery to a control extend with a smart combination of motion and focal point deflection.
To obtain the planned energy delivery ablation an optimal use of the energy may be
performed by minimizing the amplitude of the deflection by identifying the optimal
part of the motion trajectory to perform the sonications for each target points.
[0066] The sonication parameters can include as function of time, the position of focal
point (i.e., sonication trajectories), the shape of focal point (multiple or simple
focal points or any pressure distribution), the acoustic power at the focus or/and
the electrical power applied on the transducer (variable power level or use of duty
cycle).
[0067] Embodiments of the invention may include a ultrasound transducer including multiple
channels in order to control the location of the ultrasound energy delivery could
be used for this purpose. The electronic displacement of the focal point can be characterized
herein as a trajectory named "sonicated trajectory."
[0068] Embodiments of the invention may include a means to quantify motion. This may be
any imaging modality which allows quantification of the motion such as Magnetic Resonance
Imaging (MRI) or ultrasound imaging device could be used to characterize the motion.
This characterization of the motion could be also obtained by a combination of several
imaging modalities such as MRI (for the good spatial tissue contrast) and ultrasound
(for the high temporal resolution). The global displacement of the whole target or
the displacement of each points of the target volume can be used to characterize the
motion using either rigid or elastic model. The trajectories considered could be evaluated
in 1, 2 or 3 dimensions for periodic motion such as respiratory or cardiac cycle or
a-periodic motion such as muscle contraction. A model including also combination of
several type of motion could be also considered such as cardiac cycle and periodic
cycle. External sensors can also be used to identify the location within the breathing
or cardiac cycle such as respiratory bellows, cardiac ECG or VCG.
[0069] The displacement of the target point due to the motion of the tissue can be characterized
by trajectory named "motion trajectory" for this document. The use of "sonicated trajectory"
and "motion trajectory" allows to differentiate the type of target point displacement.
[0070] Fig. 8a, b, c, d and e show a subject 800 with a moving target 802. Each of the frames
a, b, c, d and e are different time periods. The transducer is shown as item 804.
The arrows or points labeled 806 shows the displacement of the moving target 802.
When the moving target 802 is within the beam deflection zone it is sonicated with
the ultrasound 808. The sonication is only performed in Figs. 8b, c and d. Fig. 8
shows the Side view of sonication of a target point moving along FH direction using
motion tracking during part of the displacement. The arrow indicates for each time
frame the tissue displacement relative to the central position.
[0071] Fig. 9 shows a top view of the same sonication that was shown in Fig. 8. Fig. 9 shows
the top view of the same sonications as in Fig. 8 of a target point moving along FH
direction using motion tracking during part of the displacement. The arrow indicates
for each time frame the tissue displacement relative to the central position.
Single point heating:
[0072] To start with a simple case, it's possible to consider the heating of a single target
tissue point (named 1) with a periodic linear motion trajectory crossing the geometric
center of transducer. As illustrated in Fig. 8 and 9, the target point can be sonicated
only during a part of the cycle to achieve the require ablation while restricting
the amplitude of deflection used.
[0073] A temperature and/or dose control algorithm can process the amount of energy E
1 to deliver on this point for a half cycle T
CYCLE/2. All this energy can't be deliver in a single brief pulse because high power level
can induce unwanted cavitation effect or because of hardware limitation such as transducer
or amplifier over-heating. Based on the knowledge of the maximal acoustic power level
P
MAX apply at the focal point (either selected by user or based on system specification),
the minimal required heating duration can be defined by T
01= E
1/P
MAX. In some cases the heating duration may need to be split into several discrete times.
For example, a target point could move in and out of the beam deflection zone as a
subject breathes. During a particular breathing cycle, the target point may not be
within the beam deflection zone long enough to complete a full treatment in half cycle
The energy to perform the complete treatment can be distributed in several cycles
with required energy E
1 to deliver that can be adjusted dynamically based on temperature and/or a thermal
dose feedback algorithm. The normalized intensity can be evaluated for each deflection
performed to reach each location of the motion trajectory of the target point. The
resulting graph will be similar to the one described in Figs. 6 and 7 except that
the normalized intensity is display as function of time rather than focal point location
as shown in Fig. 11. The relation between time and location is defined by the motion
trajectory of the target point.
[0074] Fig. 10 shows a planar representation of linear periodic motion 1000. The x-axis
is the transducer y-axis displacement 1002. The y-axis is the transducer z-axis displacement
1004. The dashed line 1006 shows the 50% normalized intensity. The dashed line 1008
shows an example of a predetermined threshold 1008. The region 1010 is a beam deflection
zone defined by line 1008. The bolded line 1012 shows the sonicated portion of the
trajectory 1000.
[0075] Fig. 11 illustrates the sonication time for the periodic motion shown in Fig. 10.
The normalized intensity is shown as a function of time 1100. The x-axis is the time
1102. The y-axis is the normalized intensity 1104. The dashed line 1006 indicates
the 50% level of intensity. The dashed line 1008 indicates the predetermined threshold
1008. When the normalized intensity is above the predetermined threshold 1008 the
target is within the beam deflection zone 1010. The period of time 1106 also labeled
T
1 is the sonication period.
[0076] Figs. 10 and 11 illustrate a planar representation of the linear periodic motion
trajectory, Fig. 10, or normalized intensity as function of time, Fig. 11, for this
trajectory. The thin solid line corresponds to the non sonicated part of the trajectory
and the thick solid line corresponds to the sonicated part of the motion trajectory.
Short and long dot line corresponds to 50% and I
1 normalized intensity threshold respectively. Transducer axis Y corresponds to the
FH direction of Figs. 8 and 9.
[0077] By performing maximal search, it's possible to find the maximal normalized intensity
threshold I
01 for which all points of the motion trajectory are above this threshold for a duration
equal to T
01 as described in Figs. 10 and 11. The reason why I
01 and T
01 are replaced by I
1 and T
1 on Figs. 10 and 11 is explained further in the text. The threshold I
1 has to be preferably selected to a value higher than 50%, otherwise excessive deflection
may be required to track the target tissue.
[0078] The sonicated part of the tissue motion trajectory, indicated Figs. 10 and 11, will
correspond to all points for which the normalized intensity is higher than I
01 (thick line). Since this part of the motion trajectory corresponds to a duration
T
01, the heating duty cycle 2T
01/ T
CYCLE will be sufficient to achieve the require heating. This selection of the part of
trajectory heated is thus the one minimizing the intensity drop due to the deflection.
The method could also consider more complex cyclic trajectory along 2 or 3 directions.
The Figs. 12 and 13 show an example of 2D displacement (which is easier to drawn than
3D displacement). However we can easily understand that the method could be interpolate
in 3 directions since the normalized intensity for each point of the motion trajectory
can be process in 3D using the same method. Also only half of the motion cycle was
considered, assuming that the other half of the cycle is identical, to simplify illustrations.
But the complete cycle can be considered if the motion trajectory is not composed
of two identical half periods such as trajectories with hysteresis.
[0079] Fig. 12 shows a case similar to that shown in Fig. 10. However in this case the planar
representation of a curved periodic motion trajectory 1200 is shown. In this example
the sonication portion of trajectory 1200 is labeled 1212.
[0080] Fig. 13 is analogous to Fig. 11. The normalized intensity is a function of time 1300
of trajectory 1200 is again shown as a function of time. The sonicated period in Fig.
13 is labeled 1306.
[0081] On the particular example displayed in Fig. 12 and 13, the motion trajectory of the
target point doesn't cross the geometric center of the transducer and thus the normalized
intensity never reaches 100% which is not mandatory for this method.
[0082] Different strategies could be used to compensate for the intensity drop. The method
the most frequently used consists to increase the electrical power applied on the
transducer by a factor inversely proportional to the normalized intensity. Thus the
intensity at the focal point can be kept constant, for example just below the cavitation
threshold.
[0083] But if the maximal power is limited by hardware limitation, for example the electrical
power apply on the transducer should not be increased, it's possible to increase the
sonications duration to a value larger than T
01.
[0084] For such duration increase, it's possible to use an iterative algorithm which takes
in to account the average normalized intensity <I>
01 over the length of the selected part of the motion trajectory. <I>
01 is a value between I
01 and 100%.
[0085] The algorithm is initiated with value described previously:
[0086] After iteration are performed base on those equations:
[0087] For each iteration, the time T
n1 is increased and thresholds I
n1 and <I>
n1 decreased. Since the time T
n1 can't overpass the half period cycle T
CYCLE/2, this problem converges. Values obtained at the convergence can be thus labeled
T
1, I
1 and <I>
1. The resulting energy deposited at the target is thus E
1=P
MAX×<I>
1×T
1.
[0088] Fig. 14 illustrates a situation similar to that shown in Fig. 10 except in this case
there are five points which are sonicated. The trajectories are each labeled 1400
and the sonicated portion of each trajectory is labeled 1412.
[0089] Fig. 15 is analogous to Fig. 11. In Fig. 15 three normalized intensity curves 1500
are shown. The portion of the curves labeled 1502 correspond to three sonication periods.
[0090] Figs. 14 and 15 show the same representation as Figs. 10 and 11 except that trajectories
of 5 points are considered; the position of each point at the middle of the target
tissue motion cycle is indicated by small white circles. This corresponds to the location
of the points in the tissue. Those 5 points are located along a circular target. The
thin solid line corresponds to the non sonicated part of the motion trajectory and
the thick solid line corresponds to the sonicated part of the motion trajectory. The
target tissue moves from the left to the right along the Y axis during the first half
of the cycle.
[0091] Fig. 16 is used to illustrate the motion shown in Figs. 14 and 15. Fig. 16 shows
a top view of the sonication of five target points moving along the FH direction using
motion tracking during part of the displacement. Fig. 16 has frames a, b, c, d and
e. Figure 16 shows a top view of sonication of 5 target points moving along FH direction
using motion tracking during part of the displacement. The arrow indicates for each
time frame the tissue displacement relative to the central position and the point
selected for sonications according to the deflection minimization illustrated in Figs.
14 and 15.
[0092] Figs. 17 and 18 show the same representation for example shown in Figs. 14 and 15
except there is higher energy deposition in each point similar maximum intensity criteria.
This increases the sonication duty cycle for each point. Figs. 17 and 18 show the
same representation as Figs. 14 and 15 with trajectories of 5 points but considering
higher energy deposition in each point with similar maximum intensity criteria, thus
increasing the sonication duty-cycle for each point.
Volumetric heating:
[0093] The method previously described for a single point can be generalized for a target
volume including several target points. A temperature and/or dose control algorithm
can process the amount of energy E
K to deliver on each point K for a half cycle T
CYCLE/2 in 2D or in 3D. Using a similar method as previously explained, the minimal required
heating duration for each point K could be defined by T
0K= E
K/P
MAX. It should be noted that more than one motion cycle is usually necessary to ablate
the entire volume (at least for larger volumes) due to hardware restrictions and also
in order to avoid causing mechanical damage that may occur at very high ultrasound
pressures.
[0094] Figs. 17 and 18 illustrates the volumetric motion tracking methods with 5 points
located along target circle. To simplify the illustration Fig. 18 with 3 curves instead
of 5 curves, it has been assumed that points 2, 5 and 3, 4 are distributes symmetrically
with identical amount of energy required and minimum heating duration. A maximal search
can be performed, to find the maximal normalized intensity threshold I
0K for which all points of the motion trajectory of the point K are above this threshold
during a duration equal to T
0K:
[0095] As illustrated in Fig. 16, it results that at the beginning of the cycle none of
the target points is and then only point 1 is sonicated, followed by points 2 and
5 that are sonicated simultaneously, followed by points 3 and 4 that are sonicated
simultaneously and at the end of the half cycle no point is sonicated. It results
that energy has been delivered in each of the 5 points of the circular sonications
trajectory, but deflection has been performed almost only along one axis orthogonal
to the motion axis.
[0096] To illustrate the fact that this method allows to deliver different amount of energy,
Figs. 17 and 18 display a similar exampled of trajectory of 5 points but delivering
twice more energy as compare to Figs. 14 and 15 by increasing the sonication duration
of each point.
[0097] Fig. 19 shows a plot of a number of points which are sonicated as a function of time.
The x-axis shows the time 1102 and the y-axis 1900 shows the number of sonicated points
as a function of time 1102. Fig. 19 shows the number of points to sonicate during
each part time part of the half cycle for the example shown in Figs. 17 and 18. However,
in some case more than one point has to be sonicated during the same period such as
the points 3 and 4. This can be performed either by forming multiple focal points
or switching very fast the focal point from one location to another. The fast switching
approach is usually preferred since it induces a lower amount of side lobes than the
multiple focus solution (resulting in addition energy loss). In both cases, the total
energy deliver by the transducer during this period has to be shared between several
points. To take into account this effect a function named
, as illustrated Fig. 19, is defined to quantify the number of point to sonicate
during each part time part of the cycle.
[0098] To compensate for the intensity drop induced by the deflection and the number of
point to sonicate in the same period, and iterative algorithm can be used. For duration
increase, it's possible to use an iterative algorithm which takes into account the
average of the normalized intensity multiply by the number of sonications <
>
K over the length of the selected part of the motion trajectory.
[0099] The algorithm is initiated with value described previously:
[0100] After iteration are performed base on those equations:
[0101] At each iteration, the time T
nK is increased and threshold I
n1 and <I>
n1 decreased. Since the time T
nK can't overpass the half period cycle T
CYCLE/2, this suite converges. Values obtained at the convergence can be thus labeled T
K, I
K and <
>
K. The resulting energy deposited at the target is thus E
1=P
MAX×<
>
1×T
1. As previously thresholds I
K have to be selected preferably to a value higher than 50%, otherway excessive deflection
would be required to track the target tissue.
[0102] Figs. 20 and 21 are analogous to Figs. 17 and 18. In Figs. 20 and 21 the resulting
sonicated trajectories after optimization of the sonication time for the example shown
in Figs. 17 and 18 taking into account the number of points sonicated simultaneously.
Figs. 20 and 21 shows the resulting sonicated trajectory after optimization of the
sonication time for the example shown figure 8 taking in to account the number of
point sonicated simultaneously. Relative to figure 8, the duration T1 was reduced
and durations T2,5 and T3,4 were increased.
[0103] For the example shown in Figs. 17 and 18, it results that the point 1 is never sonicated
during the same time period as other points and the associate high average normalized
intensity on the selected period would require a much shorter allocated sonicating
period than other points as illustrated in Figs. 20 and 21.
It should be noticed that in the examples shown in Figs. 14, 15, 17, 18, 20, and 21
the motion occurs along the axis Y with amplitude larger than the diameter of the
target circle. However the deflection performed to deliver the energy on this circle
takes place mainly along axis orthogonal to the motion. The deflection along the motion
direction is adjusted only to get sufficient energy delivery in each point. It could
be that in particular case of volumetric heating is larger than the motion amplitude,
in this case additional electronic steering is required along the direction of the
motion. Even in such case described algorithm remains exactly the same.
[0104] Figs. 22 and 23 are analogous to Figs. 20 and 21. The example illustrated in Figs.
22 and 23 is similar to that in Figs. 20 and 21 except that curve trajectories are
used instead of straight ones.
As illustrated in Figs. 22 and 23, this method can be applied using exactly the same
algorithm to curved trajectories different for each target point that would be for
example the result of elastic displacement of a deformable target organ.
For single target point as multiple target point, the required energy E
K to deliver can be adjusted dynamically based on temperature and/or thermal dose feedback
algorithm. As consequence the duration T
K, the intensity threshold I
K as well as the part of the cycle heated can be also adjusted dynamically (i.e for
each cycle).
[0105] Fig. 24 is similar to Fig. 9 except three targets 802 are being sonicated. Fig. 24
illustrates sonications of 3 target points placed along the motion axis FH while using
algorithm to minimize energy loss induced by deflection.
Enlargement of target area along the motion trajectory:
[0106] In some case it might be required to perform ablation elongated along the motion
trajectory. Such result can be obtained for example by selecting 3 points along the
motion trajectory such as the FH axis as displayed in Fig 24. As consequence of algorithm
minimizing the deflection previously described, sonications is performed successively
in each point when the target points goes in front of the transducer.
[0107] Fig. 25 is similar to Fig. 9 except a single point 802 is being sonicated without
motion tracking during half of the tissue trajectory to extend the energy delivery
to align twice shorter than the amplitude of the motion trajectory. Fig. 25 shows
sonication of a single point without motion tracking during half of the tissue trajectory
to extend the energy delivery to a line twice shorter than the amplitude of the motion
trajectory. Instead of defining several points along the motion trajectory, an alternative
algorithm minimizing energy loss induced by deflection could be considered by defining
one point only and allowing this sonicated point to spread along the motion trajectory
to a control extend. Such algorithm can identify the point of the motion trajectory
which the deflection amplitude, and keep sonicating with the same deflection during
a part of the motion trajectory in order to cover the target trajectory. As illustrated
Fig. 25, sonication is performed always at the same location relatively to the transducer
but during only half of the motion-traj ectory in order to deliver energy over a line
which is twice shorter than the amplitude of motion. Compared to the first method
illustrated Fig. 24, the second methods illustrated Fig. 25 offers the advantage to
perform more continuous energy delivery since only one point has to be consider along
the motion trajectory rather than a series of points. However the first method allows
energy delivery over a sonications trajectory larger than the motion trajectory.
[0108] Fig. 26 is similar to Fig. 9 except three points 802 are being sonicated without
motion tracking. During a duty cycle adjusted to perform energy delivery over a region
over a circular region. Fig. 26 shows the sonication of 3 points without motion tracking
with a duty cycle adjusted to perform energy delivery over a region circular region.
In the same manner as the first method, the second method can be generalized to several
points sonicated. The extension of the energy deliver along the motion direction can
be thus controlled individually for each point using different sonications duration
for each point. As shown in Fig. 26, the point 1 is used to deliver energy along a
longer line than the ones formed by points 2 and 3 in order to deposit energy over
a disc. To obtain homogenous energy delivery or energy delivered according to a controller
algorithm (for example temperature and/or dose control) the electrical power on the
transducer can be modulated as function of deflection amplitude and instantaneous
tissue displacement speed. The difference to the examples shown earlier in Figs. 14,
15, 17, 18, 20, and 21 is that there is here no electronic steering of the focal spot
along the direction of motion (i.e. the FH direction). Apart from that the sonication
methodology is exactly the same.
Cruder algorithm than the one previously described could be considered to minimize
the energy loss due to the deflection associated to the motion tracking. For example
the user can simply select a normalize intensity threshold I
T. Thus the system sonicate the tissue as long as a target point is located within
the region where the normalize intensity is higher than the threshold I
T. As a consequence the maximum energy deposit is achieved in each point with a deflection
limited to the acceptable percentage of energy loss related to deflection. Such maximal
energy deliver is useful especially for ablation in highly perfused organ, such liver
and kidney, requiring fast temperature rise.
[0109] Fig. 27 is analogous to Fig. 10 except in the example shown in Fig. 27 the sonications
are for three points with continuous linear displacement based on the normalized intensity
threshold 1008. Fig. 27 shows an example of sonications for continuous linear displacement
(non periodical) based on normalized intensity threshold region I
T. The use of algorithm which minimizes the intensity loss due to deflection can be
also applied on organs which are not following a periodic displacement, such as sudden
muscle contraction. For example Fig. 27 shows an example of continuous rigid displacement
along one axis for 3 points. Motion tacking of the 3 target points is applied unless
the intensity threshold is lower than the selected threshold I
T.
[0110] While the invention has been illustrated and described in detail in the drawings
and foregoing description, such illustration and description are to be considered
illustrative or exemplary and not restrictive; the invention is not limited to the
disclosed embodiments.
[0111] Other variations to the disclosed embodiments can be understood and effected by those
skilled in the art in practicing the claimed invention, from a study of the drawings,
the disclosure, and the appended claims. In the claims, the word "comprising" does
not exclude other elements or steps, and the indefinite article "a" or "an" does not
exclude a plurality. A single processor or other unit may fulfill the functions of
several items recited in the claims. The mere fact that certain measures are recited
in mutually different dependent claims does not indicate that a combination of these
measured cannot be used to advantage. A computer program may be stored/distributed
on a suitable medium, such as an optical storage medium or a solid-state medium supplied
together with or as part of other hardware, but may also be distributed in other forms,
such as via the Internet or other wired or wireless telecommunication systems. Any
reference signs in the claims should not be construed as limiting the scope.
LIST OF REFERENCE NUMERALS
[0112]
- 300
- therapeutic apparatus
- 301
- subject
- 302
- high intensity focused ultrasound system
- 303
- subject support
- 304
- fluid filled chamber
- 306
- ultrasound transducer
- 308
- mechanism
- 310
- mechanical actuator/power supply
- 312
- path of ultrasound
- 314
- ultrasound window
- 316
- gel pad
- 318
- sonication point
- 320
- moving target
- 322
- beam deflection zone
- 324
- computer
- 326
- hardware interface
- 328
- processor
- 330
- user interface
- 332
- computer storage
- 334
- computer memory
- 340
- treatment plan
- 342
- real time medical data
- 344
- sonication control commands
- 346
- ultrasonic calibration
- 348
- sonication duration
- 350
- control module
- 352
- sonication control command generation module
- 354
- motion tracking module
- 400
- therapeutic apparatus
- 402
- magnetic resonance imaging system
- 404
- magnet
- 406
- bore of magnet
- 408
- imaging zone
- 410
- magnetic field gradient coils
- 412
- magnetic field gradient coils power supply
- 414
- radio-frequency coil
- 416
- transceiver
- 420
- pulse sequence
- 422
- magnetic resonance thermometry pulse sequence
- 424
- magnetic resonance data
- 426
- magnetic resonance image
- 428
- temperature map
- 430
- image reconstruction module
- 432
- temperature mapping module
- 434
- image segmentation module
- 500
- therapeutic apparatus
- 502
- diagnostic ultrasound system
- 504
- diagnostic ultrasound transducer
- 506
- diagnostic ultrasound data
- 508
- diagnostic ultrasound image
- 510
- image reconstruction module
- 512
- image segmentation module
- 600
- normalized intensity
- 602
- perpendicular deflection
- 604
- normalized intensity
- 606
- 50% normalized intensity
- 608
- beam deflection zone
- 700
- normalized intensity
- 702
- deflection along beam path
- 704
- beam deflection zone
- 800
- subj ect
- 802
- moving target
- 804
- ultrasound transducer
- 806
- displacement
- 808
- ultrasound
- 1000
- planar representation of linear periodic motion trajectory
- 1002
- transducer y-axis displacement
- 1004
- transducer z-axis displacement
- 1006
- 50% normalized intensity
- 1008
- predetermined threshold (I1)
- 1010
- beam deflection zone
- 1012
- sonicated portion of trajectory
- 1100
- normalized intensity as a function of time
- 1102
- time
- 1104
- normalized intensity
- 1106
- sonication period
- 1200
- planar representation of curved period motion trajectory
- 1212
- sonicated portion of trajectory
- 1300
- normalized intensity as a function of time
- 1306
- sonication period
- 1400
- motion trajectory
- 1412
- sonicated portion of trajectory
- 1500
- normalized intensity
- 1502
- sonication period
- 2700
- motion trajectory
- 2712
- sonicated portion of trajectory
1. A therapeutic apparatus (300, 400, 500) comprising:
- a high intensity focused ultrasound system (302) comprising an ultrasound transducer
(306), wherein the ultrasound transducer has an electronically adjustable focus (318),
wherein the high intensity focused ultrasound system has a beam deflection zone (322,
608, 704, 1010, wherein the ultrasound transducer is configured for generating acoustic
power when supplied with alternating current electrical power, wherein the intensity
of ultrasound at the electronically adjustable focus divided by the acoustic power
emitted is above a predetermined threshold (606, 1008) within the beam deflection
zone;
- a memory (334) for storing machine executable instructions (350, 352, 354); and
- a processor (328) configured for controlling the therapeutic apparatus, wherein
execution of the machine executable instructions causes the processor to:
- receive (102, 202) real time medical data (342, 424, 506), wherein the real time
medical data is descriptive of the location of a moving target (320, 802);
- adjust (104, 204) the electronically adjustable focus to target the moving target
using the real time medical data; and
- sonicate (106, 206) the moving target when the moving target is within the beam
deflection zone.
2. The therapeutic apparatus of claim 1, wherein the moving target is located at least
partially using real time tracking of the target within the real time medical data.
3. The therapeutic apparatus of claim 1 or 2, wherein execution of the instructions causes
the processor to receive a motion tracking model (354), wherein the motion tracking
model is configured for predicting a location of the moving target using the real
time medical data, wherein the electronically adjustable focus is adjusted at least
partially in accordance with the location predicted by the motion tracking model.
4. The therapeutic apparatus of claim 1, 2, or 3, wherein the moving target comprises
at least one localized volume.
5. The therapeutic apparatus of claim 4, wherein the moving target comprises multiple
localized volumes, wherein the electronically adjustable focus is targeted to the
moving target by specifying a sequence of localized volumes chosen from the multiple
localized volumes, wherein execution of the instructions further cause the processor
to determine the sequence is in accordance with the real time medical data.
6. The therapeutic apparatus of claim 4 or 5, wherein execution of the instructions further
causes the processor to receive an ultrasonic calibration (346), wherein the ultrasonic
calibration is descriptive of the spatially dependent intensity of ultrasound at the
electronically adjustable focus within the beam deflection zone, wherein execution
of the instructions further causes the processor to determine a sonication duration
(348, 1106, 1306, 1502) for each localized volume in accordance with the ultrasonic
calibration and the real time medical data, wherein the therapeutic apparatus is configured
to sonicate each localized volume for the sonication duration.
7. The therapeutic apparatus of claim 1, 2, or 3, wherein the moving target comprises
at least one path.
8. The therapeutic apparatus of claim 7, wherein the electronically adjustable focus
follows a trajectory along the at least one path, wherein execution of the instructions
further cause the processor to determine the trajectory is in accordance with the
real time medical data.
9. The therapeutic apparatus of claim 7 or 8, wherein execution of the instructions further
causes the processor to receive an ultrasonic calibration (346), wherein the ultrasonic
calibration is descriptive of the spatially dependent intensity of ultrasound at the
electronically adjustable focus within the beam deflection zone, wherein each of the
at least one paths is divided into portions, wherein execution of the instructions
further causes the processor to determine a sonication (348, 1106, 1306, 1502) duration
in accordance with the ultrasonic calibration and the real time medical data for each
of the portions, wherein the therapeutic apparatus is configured to sonicate each
of the portions for the sonication duration.
10. The therapeutic apparatus of any one of the preceding claims, wherein the location
of the moving target is predicted using dynamic analysis of the real time medical
imaging data.
11. The therapeutic apparatus of any one of the preceding claims, wherein the real time
medical data is real time medical image data, wherein execution of the instructions
further causes the processor to acquire (202) the real time medical image data using
a medical imaging system (402, 502), wherein the medical imaging system is any one
of the following: a magnetic resonance imaging system (402) and a diagnostic ultrasound
imaging system (502).
12. The therapeutic apparatus of claim 11, wherein the medical image data comprises motion
data and real time thermographic data (428), wherein the moving target is located
using the motion data.
13. The therapeutic apparatus of claim 12, wherein the sonication of the moving target
is controlled in accordance with the thermographic data.
14. A method of operating a therapeutic apparatus (300, 400, 500), wherein the therapeutic
apparatus comprises a high intensity focused ultrasound system (302) comprising an
ultrasound transducer (306), wherein the ultrasound transducer has an electronically
adjustable focus (318), wherein the high intensity focused ultrasound system has a
beam deflection zone (322, 608, 704, 1010), wherein the ultrasound transducer is configured
for generating acoustic power when supplied with alternating current electrical power,
wherein the intensity of ultrasound at the electronically adjustable focus divided
by the acoustic power emitted is above a predetermined threshold (606, 1008) within
the beam deflection zone, wherein the method comprises the steps of:
- receiving (102, 202) real time medical data (342, 352, 354), wherein the real time
medical data is descriptive of the location of a moving target (320, 802);
- adjusting (104, 204) the electronically adjustable focus to target the moving target
using the real time medical data; and
- sonicating (106, 206) the moving target when the moving target is within the beam
deflection zone.
15. A computer program product comprising machine executable instructions (350, 352, 354)
for operating a therapeutic apparatus (300, 400, 500), wherein the therapeutic apparatus
comprises a high intensity focused ultrasound system (302) comprising an ultrasound
transducer (306), wherein the ultrasound transducer has an electronically adjustable
focus (318), wherein the high intensity focused ultrasound system has a beam deflection
zone (322, 608, 704, 1010), wherein the ultrasound transducer is configured for generating
acoustic power when supplied with alternating current electrical power, wherein the
intensity of ultrasound at the electronically adjustable focus divided by the acoustic
power emitted is above a predetermined threshold (606, 1008) within the beam deflection
zone, wherein the therapeutic apparatus further comprises a processor configured for
controlling the therapeutic apparatus, wherein execution of the machine executable
instructions causes the processor to:
- receive (102, 202) real time medical data (342, 424, 506), wherein the real time
medical data is descriptive of the location of a moving target (320, 802);
- adjust (104, 204) the electronically adjustable focus to target the moving target
using the real time medical data; and
- sonicate (106, 206) the moving target when the moving target is within the beam
deflection zone.